Technical Field
The present invention relates to mobile communications systems, and more particularly, heterogeneous wireless networks.
Description of the Related Art
Heterogeneous wireless networks (HetNets) are a type of mobile communications system comprising a multitude of disparate transmission points (TPs) deployed in an irregular fashion. HetNets are expected to be increasingly common wireless network systems in the future. Resource management for HetNets is typically performed within a coordination area comprising a set of TPs and a set of users that the TPs should serve. In HetNet systems having a backhaul with a relatively high latency (up to several dozens of milliseconds), coordinated resource management decisions are not able to be achieved within fine slot-level granularity which is typically a millisecond because the coordinated management requires exchanges of messages and signaling over the backhaul.
Semi-static resource management schemes wherein the resource management is performed over a set of TPs at two time scales have been developed for systems having a backhaul with a high latency and have been found to provide a more robust management. In these semi-static schemes, coordinated resource management may be performed at a coarse frame-level time-scale which is a time length at least as large as the backhaul latency. The coarse frame-level time-scale coordinated management may be based on averaged (not instantaneous) slowly varying metrics that are relevant for a period longer than the backhaul latency. Resource management may also be performed on a fine time-scale. The fine time-scale resource management may be performed independently by a TP without coordination amongst the other TPs.
Resource management for a cluster of TPs that includes multiple high power macro TPs as well as several low power pico TPs is very complicated due to the backhaul latency, irregular topology and the fact that there may not be one common dominant interferer for all TPs.
Some known resource management schemes have exploited cell dormancy in which each TP is made active or inactive for an entire frame duration. Other known resource management schemes have combined partial muting in which a single TP is made active or inactive for a time interval that is a fraction of the frame duration. The fraction of the frame duration for which a TP is active is known as the “activation fraction” of the TP. Load balancing which is also referred to as “user association” has also been implemented wherein each user is associated with a specific TP during a frame duration. However, current resource management systems and methods do not scale in an effective manner when activation fractions of all TPs have to be optimized.